Titanium in metallic form or as a compound is an important element in the chemical series. For example, titanium dioxide is utilized in paint pigments, in white rubbers and plastics, floor coverings, glassware and ceramics, painting inks, as an opacifying agent in papers, etc. The other titanium compounds are used in electronics, as fire retardants, waterproofing agents, etc. The metal may be used as such or in alloy form as structural material in aircraft, in jet engines, marine equipment, textile machinery, surgical instruments, orthopedic appliances, sporting equipment, food handling equipment, etc. Heretofore in recovering the titanium from titanium bearing sources such as ilmenite, rutile, etc., the titanium has been subjected to separation steps which involve the formation of titanium as a compound in a valence state of +4, such compounds usually involving titanium oxide. However, when attempting to separate titanium dioxide from impurities which are also contained in the ore such as iron, the hydrolysis of the titanium dioxide at elevated temperatures usually results in also obtaining relatively large amounts of iron along with the titanium.
Heretofore in the prior art various methods have been utilized to recover titanium values from titanium bearing sources. For example, in U.S. Pat. No. 3,236,596 an unroasted ilmenite ore is leached with hydrogen chloride at an elevated temperature. Following this, dissolved iron is reduced with iron or other reductants to precipitate ferrous chloride by saturating the liquor with hydrogen chloride gas. The hydrogen chloride is then extracted from the liquor by a vacuum distillation and the titanium is recovered by conventional means. Likewise, U.S. Pat. No. 3,825,419 reduces an ilmenite ore to produce ferrous oxides. The reduced ore is then leached for about 4 hours under a moderate pressure thereby dissolving the iron in the acid along with about 15% of the titanium. The iron is recovered as ferric oxide containing impurities in the spray roaster while the insoluble product which is primarily titanium dioxide but which contains all of the silica present in the original ore is recovered. U.S. Pat. No. 3,859,077 also discloses a process for recovering titanium in which a titanium tetrahalide is mixed with iron oxide in slag or a titaniferous ore at an extremely high temperature of about 1000.degree. C. to produce volatile impurity chlorides and titanium dioxide. A similar patent, U.S. Pat. No. 3,929,962, also reduces a titanium bearing ore at a high temperature to produce titanium sesquioxide which is in a form whereby it is easier to treat for a titanium-iron separation. Another prior art reference, U.S. Pat. No. 3,903,239 teaches a method for recovering titanium in which unroasted ilmenite is leached over a period of days at room temperature to recover about 80% of the titanium. Sulfur dioxide is added during the leaching to cause a precipitation of the ferrous chloride after which titanium dioxide is recovered by diluting and heating the solution.
In contradistinction to the prior art methods hereinbefore set forth for recovering titanium values from a titanium bearing source, it has now been found possible to recover the iron which is present in the source as well as recovering the titanium metal values.
This invention relates to a process for obtaining both iron metal values and titanium metal values from a bearing source which contains both iron and titanium. More specifically, the invention is concerned with a process for recovering titanium metal values and iron metal values from a titanium bearing source such as ilmenite. The advantages of utilizing the process of the present invention are found in the fact that the reactions may, if so desired, be effected at atmospheric pressure, thus obviating the use of relatively expensive and complicated equipment as well as obtaining a desired yield of titanium metal values using relatively low grade ores as a starting material. Another advantage lies in the additional recovery of iron metal values from the ore in contradistinction to other processes where such values have been lost and not recovered.
It is therefore an object of this invention to provide an improved process for the production of iron metal values and titanium metal values.
A further object of this invention is to provide a hydrometallurgical process for obtaining high yields of titanium metal values as well as recovery of iron metal values from bearing sources containing both metals.
In one aspect an embodiment of this invention resides in a process for the recovery of iron values and titanium values from an iron and titanium bearing source which comprises the steps of crushing said source, subjecting said crushed source to a reductive roast at an elevated temperature in a reducing atmosphere, leaching the resultant reduced source with a leach solution comprising a halogen-containing compound, separating insoluble gangue from the soluble metal halides, precipitating titanium dioxide from the soluble metal halides by treatment with iron oxides, separating said titanium dioxide from soluble iron halide and recovering said titanium dioxide, crystallizing the soluble iron halide in a crystallization zone, reducing one portion of said iron halide to form metallic iron and recovering the same, oxidizing the second portion of said iron halide to form iron oxides, and recycling said iron oxides to precipitate titanium dioxide.
A specific embodiment of this invention is found in a process for the recovery of iron values and titanium values from ilmenite which comprises the steps of crushing ilmenite, subjecting said crushed ilmenite to a reductive roast at a temperature in a range of from about 600.degree. to about 900.degree. C. in a reducing atmosphere, leaching the resultant reduced ilmenite with a leach solution comprising hydrogen chloride to form soluble iron chloride and soluble titanium chloride, filtering to remove the insoluble gangue, precipitating titanium dioxide from the soluble titanium chloride by treatment with ferric oxide, separating the solid titanium dioxide from soluble iron chlorides, crystallizing soluble iron chloride in a crystallization zone at a reduced temperature, reducing one portion of the iron chloride at a temperature in the range of 600.degree. to about 900.degree. C. to form metallic iron and hydrogen chloride, recycling the hydrogen chloride thus formed to the leach zone for use as a portion of the leach solution, oxidizing the second portion of the iron chloride to form ferric oxide and recycling the thus formed ferric oxide to contact with titanium chloride to form solid titanium dioxide.
Other objects and embodiments will be found in the following further detailed description of the present invention.
As hereinbefore set forth, the present invention is concerned with a process for recovering both iron metal values and titanium metal values from a metal bearing source such as ore including ilmenite, rutile, etc. By utilizing the process of the present invention, it is possible to obtain a high yield of titanium metal values while also maintaining iron metal values which heretofore have not been recovered as such. The process is effected by crushing an ore source such as ilmenite or other sources such as sand which contains the desired metals, chiefly titanium and iron as well as minor amounts of vanadium, chromium, manganese, etc., to a particle size less than about 35 mesh. Thereafter, the crushed metal bearing source is subjected to a reductive roast at an elevated temperature which will range from about 600.degree. up to about 1000.degree. C. or more and preferably in a range of from about 600.degree. to about 900.degree. C. in the presence of a reducing gas such as hydrogen, carbon monoxide, combinations of carbon monoxide and hydrogen, etc., or any other suitable reductant. The reductive roast is effected for a period of time ranging from about 0.5 up to about 2 hours or more. In the preferred embodiment of the invention, the reducing atmosphere which is used to accomplish the purpose of the roast usually comprises a mixture of about 50% carbon monoxide and 50% hydrogen, with an excess of reductant being utilized in order to completely reduce the iron which is present in the system to the metal. It is also contemplated within the scope of this invention that the crushed ore may be, if so desired, subjected to an oxidation roast prior to the reductive roast, said oxidative roast being accomplished at a temperature in the range of from about 600.degree. to about 900.degree. C. in the presence of an oxidizing atmosphere which is provided for by the presence of air or oxygen. However, it is to be understood that this step is not a necessary part of the present invention. Following the reductive roast of the metal bearing source, the source is then subjected to an aqueous hydrogen halide leach which, in the preferred embodiment of the invention, comprises an aqueous hydrogen chloride leach although other hydrogen halides such as hydrogen bromide and hydrogen iodide may also be utilized although not necessarily with equivalent results. The aforesaid leach of the metal bearing source is usually effected at a temperature which may range from about ambient up to about 110.degree. C., the preferred range being from about 80.degree. to about 100.degree. C., for a period of time ranging from about 0.25 hours up to about 1 hour or more in duration.
Following the leach of the metal bearing source which will form soluble iron halides and titanium such as ferrous chloride, titanium trichloride, etc., the mixture is subjected to a separation step in which the solid gangue is separated from the soluble metal chlorides and discarded. The separation of the solid gangue from the soluble metal chlorides may be effected in any suitable manner by means well known in the art, said means including decantation, filtration, etc. The soluble metal halides are then subjected to a precipitation step in a precipitation zone wherein the aqueous metal halides such as titanium trichloride and ferrous chloride are subjected to reaction with an iron oxide, preferably one in which the iron is present in its highest valence state such as ferric oxide. In this precipitation zone where the treatment is effected at temperatures ranging from about 80.degree. to 110.degree. C., the iron oxide such as ferric oxide will react with titanium chlorides such as titanium trichloride to form solid titanium dioxide. This compound, after separation from the soluble iron halides in a solid/liquid separation zone, will be recovered as such and may thereafter be treated to recover titanium as the metal, if so desired. Following separation of the solid titanium dioxide from the soluble ferrous chloride, the latter is passed to a crystallization zone wherein the temperature is reduced to afford crystallization of the ferrous chloride. For example, the temperature at which the crystallization or precipitation of the ferrous chloride is effected may range from about 0.degree. to slightly in excess of ambient or, in extreme cases, up to about 90.degree. C. When utilizing subambient temperatures the cooled solution is maintained in the desired subambient range by external means such as an ice bath, cooling coils, etc. After crystallization of the ferrous chloride is completed, the solids are separated from the latch liquor which may be recycled back to the leach zone. The solid ferrous chloride is recovered and a major portion of the product is subjected to a direct reduction step which is effected at an elevated temperature in the range of from about 600.degree. to about 900.degree. C. in contact with an excess of hydrogen. In this direct reduction step, the metallic iron which is produced will be in the form of powder or crystals and may be recovered as such. In addition, the hydrogen chloride which is formed during the direct reduction of the ferric chloride to metallic iron is withdrawn and recycled to the leach step of the process to make up a portion of the leach solution. While a major portion of the ferrous chloride in an amount ranging from 50% to 90% is subjected to this direct reduction, the remaining portion in an amount ranging from about 10% to about 50% is subjected to an oxidation step. In the oxidation step the ferrous chloride is treated at an elevated temperature ranging from about 300.degree. to about 800.degree. C. by contact with an oxygen-containing gas such as air or oxygen, the preferred oxidizing agent comprising air due to its greater availability and negligible cost. As in the case of the direct reduction any hydrogen chloride which may be formed during the oxidation step is recycled to the ferrous chloride crystallization zone to saturate said zone in order to insure a complete precipitation of the ferrous chloride by reducing the solubility of said compound. In the oxidation zone the reaction of the ferrous chloride with an oxidizing agent results in the formation of iron oxides such as ferrous oxide, ferric oxide, these compounds being charged to the zone containing the titanium chloride wherein said titanium chloride, which is predominantly titanium trichloride, is contacted with the iron oxides to form titanium dioxide.